3-4h should be plenty. To be honest, worst case you should just be put on a later plane with no or a small change cost. Obviously this depends upon how many flights there are and if you have to fly a non-major airline in to avoid the obscene one way costs lots (BA/AC etc.. charge).
I'd aim to get into Toronto by noon I'd say, AC does 14:45, 17:05 and 22:25 currently into Saskatoon in October. If cost isn't an issue book the 17:05 in business class and they'll put you on free standby for the 14:45 if you make it through faster, normally. Subject to loads.
Note that you will also need to collect your luggage at Toronto and clear customs as well. You'll likely find your luggage is sitting somewhere around the side of the room once you get through immigration unless you make it through extremely fast. Once you have the luggage proceed to connections for them to re-check your luggage onto Saskatoon. Even if the first airport lists YXE as your last destination you MUST collect it, clear customs, and re-check it at Pearson. If for any reason any of your luggage does not appear do NOT leave the baggage area before speaking to a airline rep and filling in the forms as customs will need that and you'll need to arrange for delivery once they find it. Toronto Pearson airport is recently having baggage issues, there were 15-20 people in the queue last weekend.
PR card forms are done by the landing agent, you just need your COPR, passports, and PoF/PoE (both if you have a job and if relevant). PoF is the most critical one, most people I know who've gone through recently were asked for them.
SIN cards can be gotten at Toronto airport I've heard, where wasn't obvious to me though I landed at T3 (not T1, the more major one) and I really don't think you'll want to do that in Toronto anyway. Not even sure if you can when your landing location is a different province as I believe SIN numbers vary in format (ON ones start with a 5, I assume SK ones don't?).
I'd wait until you get into Saskatoon, you'll likely find short lines there, but generally speaking check the offices online and they list their quiet hours - normally right as they open is best.
Hope this helps, let me know if you need more info, and post an update when you land
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I'll be in the Toronto airport October 1st and 8th